Chances are you’re not (yet) tracking your employees with GPS (global positioning system) devices, regardless of whether they’re driving your vehicles or their own. But it’s a technology—like social media—that’s up and coming, very fast. And, it has major implications for the world of work.

GPS tracking: what’s OK and what’s not? Bradford LeHew, an attorney with labor and employment firm Fisher & Phillips in its Chicago office, discussed those implications with us. He turned first to a pair of test cases that may—or may not—point the way to the future. The first one is a U.S. Supreme Court ruling that, oddly, has nothing to do with employment.

In U.S. v. Jones, which was decided in January 2012, the federal government suspected an individual was dealing drugs. So the government attached a GPS unit to his car—and that brought the desired results. He was arrested and prosecuted. But he sued, charging that the GPS-obtained evidence shouldn’t have been admitted into court. And, on appeal from the D.C. Circuit, the justices ruled unanimously that the GPS unit constituted a search under the Fourth Amendment. They wrote that the government “physically occupied private property for the purpose of obtaining information.” The justices all agreed that the government had invaded an area where Jones had a reasonable expectation of privacy. But you can almost hear them struggling to apply a 21st century technology to constitutional principles that are hundreds of years old.

Justice Sonya Sotomayor wrote, “GPS monitoring generates a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations.” In general, justices agreed that in some ways, being tracked in one’s car by GPS is not substantially different from being followed by a police car. But, added Sotomayor, “because GPS monitoring is cheap in comparison to conventional surveillance techniques and by design, proceeds surreptitiously, it evades the ordinary checks that constrain abusive law enforcement practices: limited police resources and community hostility.”

Here’s another personal car case. Just before the ruling in Jones, a New York appeals court decided, in Cunningham v. New York State Department of Labor, that, given the particular circumstances of the case, the state had a right to install a GPS unit on its employee’s personal vehicle. The employer suspected Cunningham of falsifying time sheets and taking unauthorized absences from work. It tried unsuccessfully to have the employee tailed by an investigator and asked and received state permission for GPS.

The state attorney general’s office placed devices on Cunningham’s car and used the resulting data to report that he often submitted fraudulent time records. He sued, charging illegal use of GPS data. But in court, judges ruled 3-2 that the use of the devices was not unreasonable, given the situation.

The majority listed these reasons for its conclusion: Traditional methods (tailing him) had failed; the employee knew he been warned about his poor performance and shouldn’t have been surprised by the data gathering; and the devices used did not constantly monitor. (The two dissenting judges noted that the devices had tracked the employee for a month, including during a week-long family vacation; they felt he had been unconstitutionally searched.) And a similar case was decided in the employer’s favor in New Jersey last year: Like Cunningham’s employer, it had tried, and failed, to have the employee tailed and so had placed a device on his personal car.

What about employer-owned vehicles? Here, says LeHew, the answers are not much clearer. He notes that one package delivery company installed GPS units on part of its fleet in order to identify which delivery routes were the most efficient. That use was clearly perfectly legal—especially since the affected drivers were informed of the employer’s research. In a way, says LeHew, vehicles are not much different from company-owned computers, phones, and e-mail: Employees should have no expectation of privacy in using any of them.

He believes there’s little question employers have the right to make sure their employees are performing company tasks on company time. And, tracking can be tied to legitimate business such as verifying attendance at scheduled meetings or training.

What should employers do? LeHew stresses that any organization that anticipates using employee tracking should create a clear and thorough policy: Most of all, it should make employees aware that their whereabouts may be monitored. Identify the employer interests to be served by using GPS technology. And, narrowly tailor the policy to serve those interests and avoid encroaching on employee privacy during nonwork hours.

Consider instructing employees to activate the vehicle technology during work hours and disable it when they’re off duty. When training managers, urge them not to overuse the tracking. How to ensure employees aren’t using their company cars for personal errands? LeHew suggests having them submit weekly mileage logs that can be checked against the car’s odometer.